The most commonly used method of producing liquid pig iron from iron ore is the blast furnace process. The resultant pig iron contains about 3 to 4.5% carbon together with other desirable or undesirable elements. These additives must be partly removed in a subsequent process in a steel converter if steel is to be produced from the pig iron. Current interest in non-blast reduction processes has been based upon potentially lower capital investment and more flexible operating conditions, especially since the apparatuses used in blast processes (e.g., blast furnaces, sinter plants, and coke oven plants) are all expensive in construction and operation. In known state-of-the art non-blast processes, iron ore is reduced to sponge iron in an ore reduction column or shaft furnace by the action of a reduction gas derived from a melting vessel located below said ore reduction apparatus. Said sponge iron is then supplied to the melting vessel where it is melted and completely reduced by adding a carbon-containing fuel and oxygen-containing gas. Such processes are disclosed, for instance, in U.S. Pat. Nos. 4,725,308, 4,579,558; 4,566,904; 4,316,739; 4,317,677. The economic disadvantages of said processes lie in the fact that a non-blast furnace includes two vertically-spaced separate apparatuses occupying a large total volume and having a relatively small horizontal area that detracts from specific throughput and limits maximum throughput. Furthermore, the non-blast process disclosed in U.S. Pat. No. 4,566,904--Bogdandy et al makes it possible to use coal with a lower energy or coal with a high portion of volatile components. This is achieved by means of injecting powdered coal and oxygen-containing gas into the melted material from the bottom of the melting apparatus, while oxygen is injected at the same time above the melted material to cause a postburning of produced reaction gas, providing additional heat transfer. However, such heat transfer is limited because the melted material is disposed on a relatively small area in relatively great depth. Therefore, the velocity of the reactions in the melted material are relatively slow, which results in limited throughput per unit of volume. Further, large heat losses are incurred because of the necessity to cool reduction gases to about 900 degrees C before introducing such gases into the ore reduction apparatus to prevent the produced solid particles of sponge iron from such overheating as might result in blocking the passage between the two apparatuses. For instance, in the above mentioned Bogdandy et al U.S. Pat. No. 4,566,904, the reduction gas that is removed from the melting apparatus is cooled from 1500 degrees C. to 900 degrees C.
Furthermore, prior non-blast processes consisting of ore reduction and melting steps have typically been concerned with production of pig iron only. For production of steel melt or nearly pure iron, pig iron is subjected to a refining operation that is now mainly a top-blown oxygen process carried out in a converter which is supplied with a lance for injecting oxygen into the melt. During transportation of the pig iron in a ladle and its charging into said converter, heat losses are inevitable. Moreover, copious fumes in the form of iron oxide particles around a micrometer in size are evolved during the oxygen blow. Such fume loss amounts to 2 to 3% of the metallic charge and thus represents an unduly large expense in such a plant.
Modern production of cast iron includes melting of pig iron with selected scrap, coke and fluxes in a cupola furnace. The latter is basically the same in design as the blast furnace, but it is about one fourth as large. The main disadvantage of such a process lies in the fact that the pig iron needs to be remelted and, therefore, additional considerable heat consumption is required.